Electroconductive paper

ABSTRACT

A technique for increasing the electroconductivity of paper is disclosed. The paper substrate is subjected to an electrical discharge which produces localized dielectric breakdown in the thickness direction.

United States Patent 1 M-atsumoto et al.

ELECTROCONDUCTIVE PAPER Inventors: Seiji Matsumoto; Satoru Honjo,

both of Asaka, Japan Xerox Corporation, Stamford, Conn.

Filed: Oct. 14, 1970 Appl. No.: 80,549

Assignee:

Foreign Application Priority Data Dec. 4, 1969 Japan 44/97341 U.S. Cl. 204/165, 8/114.6, 204/323 Int. Cl. GOld 5/12 Field of Search 204/164, 165, 323-328;

References Cited UNITED STATES PATENTS 11/1948 Young 8/2 X Nov. 13, 1973 2,977,475 3/1961 Kassenbeck 204/165 UX 3,008,888 11/1961 Fujimoto ct a1. 204/165 3,399,252 8/1968 3,553,000 1/1971 2,662,803 12/1953 2,707,744 5/1955 3,285,696 ll/1966 3,399,252 8/1968 3,540,848 11/1970 Krugler et a1. 23/209.1 F X Primary ExaminerF. C. Edmundson Attorney-Paul M. Enlow, James .J. Ralabate, Albert A. Mahassel and Peter H. Kondo [57] ABSTRACT A technique for increasing the electroconductivity of paper is disclosed. The paper substrate is subjected to an electrical discharge which produces localized dielectric breakdown in the thickness direction.

4 Claims, 2 Drawing Figures Patented Nov .13, 1973 INVENTORS SEIJI MATSUMOTO BY SATORU HONJO MMQKWZ ATTORNEY ELECTROCONDUCTIVE PAPER This invention relates to a method of preparing electroconductive paper and more specifically to a process for producing paper adaptable for use in electrophotography, and in electrostatic and electroconductive recording.

Ordinary paper which consists primarily of cellulose fibers, fillers such as clay, and hydrophobic sizing agents such as rosin, generally exhibits a relatively high electrical resistance. The value of this resistance generally varies considerably with ambient conditions, specifically the relative humidity of the atmosphere. However, in most instances the resistance value is considered too high to utilize the paper for electroconductive purposes.

Several techniques are known forincreasing the electroconductivity of paper. Most of the approaches followed employ the addition of materials into the paper structure capable of lowering electrical or electric resistance, particularly under high humidity conditions. Generally, the addition of these materials takes place during the production of the paper itself. In situations where electrophotographic reproduction of continuous tone images is required the electric resistance of the base paper should desirably be as low as possible. The necessary properties are generally realized by loading the particular paper with carbon black. In still another approach to increasing the electric conductivity of paper, electroconductive layers of carbon black have been applied to one or both surfaces of the base paper. Still another approach for achieving the increase in electric conductivity in the thickness direction across a paper substrate is set out in US. Pat. No. 3,118,789. Electroconductive short circuit paths are made throughout the paper support by making pinholes at equal intervals on a sheet of paper and filling the resulting pin holes with a carbon paint.

While the above systems have been found acceptable for the preparation of electroconductive papers there are a number of disadvantages to their particular uses. For example, in those situations where conductive materials are added to the paper in order to achieve the desired effect the introduction of these additives must be made during the paper milling process. Therefore, unless the paper is specifically being made for this restricted use, a readily available paper otherwise prepared cannot be used where such electroconductive properties are required. Further, many of the papers prepared according to these procedures are not effective under ambient conditions of low humidity. Furthermore, the utilization of carbon black for the purposes described above lend undesirable appearances to the resulting paper which is not acceptable in many instances. Where specific layersare applied to either or both of the surfaces of the base paper, special grounding techniques must be introduced during processing to facilitate utility of the resulting layered structure. The pinhole approach involved as discused above intro duces procedures not suitable for industrial applications.

Therefore, it is an object of this invention to provide a technique for preparing electrical conductive paper which will overcome the above noted disadvantages.

It is a further object of this invention to provide a novel method for the preparation of electrical conductive paper.

Still, a further object of this invention is to provide an expedient, readily adaptable technique for converting an ordinarily prepared and available paper substrate for use where low electrical resistance is required.

Yet, still a further object of this invention is to pro vide a process for producing electroconductive paper adapted for use as an electrostatic and electroconductive recording material.

Another object of this invention is to provide an electroconductive paper support having sufficiently high electroconductivity in the thickness direction.

The foregoing objects and others are accomplished in accordance with the present invention, generally speaking by bringing about a local dielectric breakdown by the application of high potential to a paper substrate or base thereby producing a short circuit path within the normally high resistant paper. Conventional paper stocks subjected to corona discharge by a corona electrode located in close proximity thereto shows local dielectric breakdown manifested in the form of black dots thereby producing densely distributed microscopic carbonized electroconductive'paths through the paper in the thickness direction. Upon making measurements following the applications of the discharge, resistance decreases in the order of 10* ohms-centimeter in the thickness direction are detectable. The treatment of the paper support can be achieved by any suitable means such as by corona discharge or by applying a high potential to electrodes holding the paper, such as electroconductive rubber rolls.

The invention is illustrated by the accompanying drawings in which:

FIG. 1 represents a schematic drawing demonstrating a specific embodiment of the present invention; and

FIG. 2 is a schematic drawing representing an alternate process implementing the concept of the present invention.

Referring now to FIG. I there is seen conventional stock paper identified as 21 which is to be processed so as to exhibit an increase in electroconductivity over substantially the entire structure having a uniformity in density. Rollers 22 and 23 are driven by any suitable driving means in the direction indicated by the arrows 27 to transport the paper support 21 in the direction indicated by the arrow 26. The roller 22 is electrocon ductive and is generally made up of a metallic material such as aluminum, steel, copper or other similar material. The roller 23 is also composed of an electroconductive component such as is described above. In addition, a semi-conductive peripheral portion 24 comprising a semi-conductive material, such as semiconductive rubber, polystyrene, polytetrachloroethylene, polyvinylfluoride, polyethyleneterephthalate, and cellulose acetate is provided. Generally, any suitable semi-conductive material having a resistivity of about 10 ohms-centimeter or greater is desired. Preferably, a resistivity between about 10 to 10 ohms-centimeter is preferred to assure obtaining the desired effect. Power source 25 supplies the potential necessary to bring about the dielectric breakdown of the paper support which generally will be in the magnitude of from about I to 5 kilovolts.

The high electrical potential is applied across the roller configuration to bring about local dielectric breakdown of the respective paper support material thereby producing the above discussed black dots. The presence of the semi-conductive material has been observed to prevent the lowering of potential during the formation of the selective black dots or the dielectric breakdown of the paper support material. The passing of the paper support through the rotating roller electrodes allows for the uniform production of the carbonized areas throughout the entire paper support.

The high potential source 25 may supply either direct or alternating current. The amount of potential applied and final value of resistance obtained will be determined by the particular species of paper worked on and the translating speed at which the paper passes through the rollers.

In an alternate embodiment of the present invention as representedby FIG. 2 a paper support 31 is subjected to a high electric potential by a group of lever electrodes 33. The paper. support 31 is translated by means of a roller system (not shown) in the direction of arrow 38. The electrodes 33 are preferably provided in the transversal direction with respect to the paper support with spacing intervals between about 0.2 to 3 centimeters. The electrodes 33 are pressed against the paper support 31 by means of a flexible elctroconductive support means 34 which are in turn mounted on an insulating support 35 and connected to a high potential source 37 through a resistance 36. The circuit is completed by connecting power source 37 to a rear electrode 32 which, in combination with electrodes 33, holds the paper support in position and produces the desired effect. Dielectric breakdown caused by the applied electric potential to the paper support forms the characteristic black dots. The resistance element 36 present in the system are utilized as a control. The resistance values are increased when the potential supply from the electric source is high and conversely it is lowered when necessary such as when the potential applied is decreased or when the translating speed for the paper support is rapid. Further, the potential of the power source 37 and the resistance values 36 will be determined appropriately according to the quality of the support paper being treated as well as the translating speed of the support paper since excessively high potential or excessively low resistance will result in the formation of a hole in the support. On the other hand if the potential is excessively low or resistance excessively high the effect desired from the discharge will not be realized or the density produced by thedischarge will be lowered to an undesirable level. Resistance levels ranging from about 10 to about 10 ohms-centimeter have produced satisfactory results.

when using a paper support one surface of which has already been subjected to an'electroconductive treatment, it is necessary that thetreated surface be contactedwith the electroconductive roller 22 in the case of FIG. 1 or with the rear electrode 32 in the embodiment presented in FIG. 2.

In addition to the steps used to carry out the process of the present invention other steps and modifications may be used if desirable. In addition, other materials may be incorporated in the treated paper and substrate or other prior art modifications may be made which will enhance, synergize or otherwise desirably effect the ultimate effect realized.

Anyone skilled in the art may have other modifications occur to him based on the teachings of the present invention. These modifications are intended to be encompassed within the scope of this invention.

What is claimed is:

l. A method for preparing electroconductive paper adapted for use as an electrostatic and electroconduc' tive recording material comprising providing a paper substrate, and applying a potential of from 1-5 kv to said paper substrate in the form of an electrical discharge thereby bringing about a local dielectric breakdown and the formation of densely distributed microscopic carbonized electroconductive paths manifested in the form of black dots which penetrate through said paper in the thickness direction.

2. The process as disclosed in claim 1 wherein said effect is realized by the application of a corona discharge.

3. The process as disclosed in claim 1 wherein the source of said high potential supplies direct current.

4. The process as disclosed in claim 1 wherein the source of potential supplies alternating current. 

2. The process as disclosed In claim 1 wherein said effect is realized by the application of a corona discharge.
 3. The process as disclosed in claim 1 wherein the source of said high potential supplies direct current.
 4. The process as disclosed in claim 1 wherein the source of potential supplies alternating current. 